Regulated cell death is an important process for elimination of specific cells in multicellular organisms during normal development and homeostasis. Deregulated cell death can lead to degenerative diseases such as Alzheimer's and Parkinson's disease and AIDS. Inhibition of cell death can also lead to oncogenesis and resistance to chemotherapeutic treatments. The E1B 19 kD protein of human adenovirus (Ad) is an important member of a class of proteins involved in suppression of cell death. It promotes the survival of cells infected with adenovirus or exposed to several external cell death (apoptosis)-inducing stimuli. The 19 kD protein is functionally similar to the Bc1-2 protooncoprotein and the Epstein-Barr virus BHRF1 protein. The 19 kD and Bcl-2 proteins appear to share common sequence motifs essential for inhibition of cell death. We have identified and cloned four cellular proteins that interact with the 19 kD (19-kD-interacting proteins, Nip1 to 4) and the Bc1-2 proteins through these homologous sequence motifs. To elucidate the common mechanism of cell death inhibition by the 19 kD and Bc1-2 proteins, we propose to functionally characterize the various Nips. The role of these cellular proteins in regulating cell death induced by different mechanisms will be examined using multiple cell death/survival assays. Endogenous expression and subcellular localization of these proteins in response to exposure to various cell death stimuli will be examined. Some of these cellular proteins contain intriguing sequence homologies. Nip1 shares limited homology with the catalytic domain of certain mammalian phosphodiesterases. Nip2 shares homology with the (GTPase- stimulating protein RhoGAP. Nip3 is localized in the mitochondria. Nip2 and Nip4 contain putative Ca2+ -binding motifs. These proteins will be characterized to elucidate their role in signal transduction and calcium mobilization. Since the cell death effectors induced by adenovirus infection is not known, we propose to use a cell free in vitro cell death system to identify and clone such effector(s). Since inactivation of survival-promoting activities of the 19 kD and Bc1-2 proteins would be advantageous, we propose to explore the possibility of using mutants defective in the survival domains as dominant negative inhibitors. Similarly, peptides corresponding to the survival domains will also be examined as competitive inhibitors of the 19 kD and Bc1-2 proteins. Thus, our proposal may illuminate the mechanism by which the 19 kD and Bc1-2 proteins suppress cell death and also reveal strategies to interfere with their activities.